But the reforms at the heart of the UPPs – neighbourhood occupations, proximity policing and use of non-lethal force – began to deteriorate after the 2016 Rio Olympics, and crime is once again spiking in Rio’s favelas.

I believe that’s because organised crime, stray bullets and aggressive policing are mutually reinforcing. Pitting police against gangs in an overt turf war has spawned a mini arms race, with all sides – from drug dealers to beat officers – resorting to ever-higher calibre weaponry.

With the recent arrival of 8,500 soldiers to go after gangs and illegal weapons in Rio de Janeiro, the twelfth military deployment there since the early 1990s, the violence could escalate further still. Brazil’s minister of defence has described the armed forces as an “anaesthetic” for the city.

On July 2 2017, the Rio de Janeiro state civil police announced that 632 people had died in crossfire this year. On average, then, the official statistic is that a Rio resident is hit by a stray bullet every seven hours.

Caught in the fogo cruzado

The actual number is likely considerably higher.

Most law enforcement and public health specialists limit the application of the term to instances when a bullet escapes the immediate scene of a shooting and results in a fatal or non-fatal injury. This narrow definition leaves out the many instances where shots are fired but no casualties are reported.

In 2015, the local newspaper Extra challenged the way the city’s Institute for Public Safety (ISP) counted stray bullets, accusing officials of dramatically under-reporting. Applying the government’s categorisation scheme, reporters found just 160 stray bullet incidents between January and June 2014, leaving another reported 39 crossfire deaths and 194 stray bullet injuries uncounted.

The media, too, under-reports on stray bullet incidents. According to a 2016 United Nations-sponsored study that tracked the “stray bullet incidents” documented in news outlets across Latin America, Brazil ranked first for crossfire-related injuries and deaths in 2014 and 2015, with 197 incidents (98 deaths and 115 injuries).

It was followed by Mexico (116 cases) and Colombia (101 cases). In all three homicide-beset nations, this is surely a low estimate.

To fill these information gaps, activists in Rio de Janeiro have developed apps. Amnesty Brazil’s Fogo Cruzado (Crossfire) has reported more than 2,000 shooting in the last 120 days, an average of 16 a day.

Press play below to see all reported shots fired in Rio from January through June 2017:

But crowd-sourcing platforms have their weaknesses, too. They rely on citizens to file reports online, meaning better coverage in more tech-savvy neighbourhoods. They also capture all incidents, both verified and unverified.

Don’t shoot

Ambiguous definitions and under-counting mean that violence analysts like me don’t actually know whether crossfire killings are on the rise.

Such reforms would require better police training and more oversight of errant officers, though, something that Rio’s underfunded and overstressed police force cannot do without able leadership and additional resources.